I'm hoping that someone might be able to help me to understand a pattern for knitting the sleeves on a hoodie. I've recently started teaching myself to knit and my inexperience is showing as I can't make sense of the instructions at all!

OK, so, I've cast on 38 stitches with 7mm needles and worked 12 rows in the cable pattern as specified. Then I've changed to 8mm needles and worked row 13.
The instructions (following the middle size) go on to say:
Rep rows 13 to 24 as given for back, at the same time inc 1 st at each end of the foll 4th and 0 (0:1) foll 4th rows [36 (40:46) sts], then on the 9 (10:10) foll 6th rows [54 (60:66) sts],working patt into inc sts.
Cont straight until sleeve measures 44 (46:47) cm from beg.

I can't quite understand what it wants me to do.
a) when i'm repeating 13 - 24, i presume i increase a stitch at either end of row 17 (the 4th row following) then row 21 (the 4th row after that). I make that a total increase of 4 stitches by the time I get to row 24. So how can I go from having 38 stitches on my needle to 40?
b) what does "and 0 (0:1) foll 4th rows" mean? Do I just ignore this bit entirely, because it says 0 for the middle size?
c) Does "cont straight etc. etc." mean that I then stop adding extra stitches and continue up in a straight line until the work is the required length?

Sorry for the length of this post and for asking a question that has been asked a million times before in as many different ways.
I hope that someone can give me some guidance (please!) as I'm desperate to finish this lovely hoodie and I'm feeling very frustrated by my inadequacy.

You inc on BOTH ends of the row, so there's 2 incs per row. First inc row takes you from 38, to 40, then on the next one it's 42, and so on and you end up with 54 sts when you're done with the increases. When there's a 0 for your size, skip it and go on to the next instruction. 'Cont straight' means just that - no more incs, work on the sts you have in the stitch pattern. You've got it pretty well figured out I think, just remember to inc at the beg and end of the row.

Thank you very much. I'm grateful for your help.
I suppose I just needed a pointer in the right direction and a bit of reassurance that I'm not quite as lost as I thought I was. I'm going to give it a go now.